Western U.S. Faces Drought Crisis, Warming Study Says

Richard A. Lovett
for National Geographic News
January 31, 2008

The U.S. West will see devastating droughts as global warming reduces the amount of mountain snow and causes the snow that does fall to melt earlier in the year, a new study says.

By storing moisture in the form of snow, mountains act as huge natural reservoirs, releasing water into rivers long into the summer dry season.

"We're losing that reservoir," said research leader Tim Barnett, an oceanographer and climate researcher at the University of California, San Diego.

"Spring runoff is getting earlier and earlier in the year, so you have to let water go over the dams into the ocean."

Summers are also becoming hotter and longer. "That dries things out more and leads to fires," Barnett added.

"Our results are not good news for those living in the western United States," the scientists write in their report, which appears in today's online edition of the journal Science.

Unnatural Changes

Barnett and his team used computer models to study water flow in Western rivers over the past 50 years.

The researchers found that the changes currently affecting the U.S. West have less than a one percent chance of being due to natural variability, Barnett told National Geographic News.

His team verified that by running a variety of control tests under pre-industrial conditions that mimicked known natural cycles.

(Related: "Ancient "Megadroughts" Struck U.S. West, Could Happen Again, Study Suggests" [May 24, 2007].)

What's been occurring recently, he said, is different from natural variability and is driven by the buildup of greenhouse gases such as carbon dioxide in Earth's atmosphere.

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